The production of light olefins, ethylene and propylene, are used in the production of polyethylene and polypropylene, which are among the most commonly manufactured plastics today. Other uses for ethylene and propylene include the production of other chemicals. Examples include vinyl monomer, vinyl chloride, ethylene oxide, ethylbenzene, cumene, and alcohols. The production of ethylene and propylene is chiefly performed by the cracking of heavier hydrocarbons. The cracking process includes stream cracking of lighter hydrocarbons and catalytic cracking of heavier hydrocarbon feedstocks, such as gas oils, atmospheric resid and other heavy hydrocarbon streams.
Currently, the majority of light olefins production is from steam cracking and fluid catalytic cracking (FCC). To enhance propylene yields from FCC, shape selective additives are used in conjunction with conventional FCC catalysts comprising Y-zeolites. However, the demand for light olefins is still growing and other means of increasing the production of light olefins have been sought. Other means include paraffin dehydrogenation, which represents an alternative route to light olefins and is described in U.S. Pat. No. 3,978,150. More recently, the desire for alternative, non-petroleum based feeds for light olefin production has led to the use of oxygenates such as alcohols and, more particularly, methanol, ethanol, and higher alcohols or their derivatives. Methanol, in particular, is useful in a methanol-to-olefin (MTO) conversion process described, for example, in U.S. Pat. No. 5,914,433. The yield of light olefins from such a process may be improved using olefin cracking to convert some or all of the C4+, MTO product in an olefin cracking reactor, as described in U.S. Pat. No. 7,268,265. Other processes for the generation of light olefins involve high severity catalytic cracking of naphtha and other hydrocarbon fractions. A catalytic naphtha cracking process of commercial importance is described in U.S. Pat. No. 6,867,341.
Despite the variety of methods for generating light olefins industrially, the demand for ethylene and propylene is still increasing and is expected to continue. A need therefore exists for new methods that can economically increase light olefin yields from existing sources of both straight-run and processed hydrocarbon streams.